The present invention relates in general to a frequency modulated radio frequency synchronous repeater system for the transmission of frequency modulated broadcast signals, and more particularly to a frequency modulated radio frequency repeater system employing a synchronous frequency modulated booster system for the re-transmission of frequency modulated broadcast signals.
Frequency modulated broadcast transmissions have been limited to audiences within a reception area. In order to increase the reception area for the frequency modulated broadcast transmission to reach a greater audience, re-transmission sites have been installed in areas remotely located from the originating transmitter. At the re-transmission sites were booster transmitters and synchronous transmitter exciters to increase the power level of the frequency modulated broadcast signals at a re-transmission site.
Heretofore, a demodulation process was used at a re-transmission site which caused frequency discrepancies, phase shifts, delays and inconsistent modulation levels between the originating frequency modulated broadcast signal and the frequency modulated broadcast signal at the re-transmission site. Phase shifts, frequency discrepancies, delays and inconsistent modulation levels between the originating frequency modulated radio frequency signal and the re-transmitted frequency modulated radio frequency signal resulted in signal degradation and noise interference in the coverage area intended for improvement by the re-transmitted frequency modulated broadcast signal of the booster transmitter.
Heretofore, a device was employed to produce a reference signal for synchronizing and stabilizing the output of frequency modulated radio frequency signals transmitted at a re-transmission booster site. The device did not use a reference signal generated at the site of the originating transmitter or re-use the FM modulation in the original carrier. Hence, the output of the frequency modulated radio frequency signal of the transmitter at the re-transmission booster site was modified from the original FM signal in frequency and in phase.
In the U.S. Pat. No. to Wu et al., 4,710,970, issued on Dec. 1, 1987, for Method Of And Apparatus For Generating A Frequency Modulated Ultrahigh Frequency Radio Transmission Signal, there is disclosed an ultra high radio frequency transmitter. The output of a very high frequency voltage controlled generator is phase locked through a phase detector with a voltage controlled crystal oscillator producing a reference signal for the stabilizing of the output transmission frequency of the ultra high radio frequency transmission frequency oscillator.
In the U.S. Pat. No. to Martinez, 4,208,630, issued on June 17, 1980, for Narrow Band Paging Or Control Radio System, there is disclosed a radio system for paging in which a central transmitting device and remote receiving devices are phase locked to a local broadcast station radio frequency carrier so as to provide a means to synchronize the transmitting device with the receiving device.
The British Patent to McGraw-Edison Company, No. 2,061,581B, published on May 18, 1983, for Communication System For Distribution Automation And Remote Metering, discloses a phase detector to which is applied the output of a limiter-amplifier and a reference signal from a voltage controlled crystal oscillator. The output of the phase detector is a control signal which is proportional to the phase differences of the input signals to the phase detector. The error signal is applied to the voltage controlled crystal oscillator. The circuit described is part of a phase locked loop circuit.
In an article published by Omega International of Irvine, Calif., entitled Synchronous Repeaters, there is mentioned that the output frequency of a booster is phase locked with the originating station through analog simulation of a digital control signal derived from the originating station.
Heretofore, FM exciters were sold to accept the composite baseband signal from a stero generator, and STL system or monaural audio and SCA programming, and to generate its operating frequency with a digitally programmed, phase-locked frequency synthesis system. Such an FM exciter was sold by Continental Electronics Mfg. Co. of Dallas, Tex., as the Continental Type 802A FM exciter, and by Broadcast Electronics of Quincy, Ill., as the Model FX-30.